1. Field of the Invention
The invention relates to a belt conveyor and particularly to a continuous belt type having a trough-shaped upper run and a horizontal return run. More particularly the invention relates to an idler construction for such conveyors which has a low-friction belt supporting surface that is free of moving parts and highly resistant to wear and corrosion.
2. Description of the Prior Art
Belt conveyors are used in numerous installations for conveying articles between stations in which the belt is an endless loop with power-driven rollers for moving the belt located at one or both ends of the conveyor. A plurality of idlers are spaced longitudinally along the path of the belt between the power-driven roller or rollers for slidably supporting both the upper troughing load-bearing run of the belt and the lower return run of the belt.
Many of these idlers use a belt engaging member for the upper run which is flexible and which conforms to the catenary configuration of the belt. The ends of these supporting members are rotatably mounted in bearings, trunnions or other mechanisms. These mountings must be continuously lubricated to enable the idler member to rotate freely in order to provide a low-friction support for the belt so that the belt may be driven smoothly, quietly and with minimum friction to reduce the power requirements of the conveyor system and to increase the amount of load which can be carried by the conveyor.
Such continuous belt conveyors are used extensively in extremely corrosive and in high-pollution environments such as coal and salt mines, steel mills, sanitary disposal plants and the like. Such environment requires continuous lubrication and maintenance of the bearings or idler supports to permit their smooth operation. These conditions increase considerably the initial cost of the conveyor system due to the expensive bearings or other support members required to withstand such conditions, as well as increasing the amount of maintenance required to insure their continuous smooth running operation. Also, the bearings must be replaced periodically with new bearings due to this corrosive environment, which replacement increases the cost of the conveyor system.
Various conveyor constructions have been developed in an attempt to reduce these problems in which the bearings, which are the main problems, are eliminated from the idler. One example of such a construction is shown in U.S. Pat. No. 2,702,115 in which an oil-filled sleeve is rotatably mounted on an internal bar. The bar is preformed with a catenary configuration and is fixedly mounted on its ends to a supporting structure. Other conveyor constructions such as shown in U.S. Pat. Nos. 2,866,538, 3,265,192, 3,311,222 and 3,885,837 are formed with a strip or strips of low-friction materials which extend longitudinally along the edges or mid-points of the moving conveyor element to provide a low-friction, load-supporting surface.
Other constructions, such as shown in U.S. Pat. Nos. 3,491,873, 3,603,450, 3,788,457 and 4,008,801, use low-friction strips as side guide rails or as actual portions of the lower belt surfaces in order to reduce the friction between the belt and/or article being conveyed and the supporting members. U.S. Pat. No. 3,955,668 discloses another type of conveyor having a continuous load-supporting pan or base with a plurality of longitudinally spaced, transversely-extending, low-friction strips located between adjacent base sections to assist in reducing the belt friction.
Most of these constructions are intended for use in applications having relatively short conveyor runs for carrying a particular type of material or article requiring a continuous rigid support over which a belt moves in transporting such materials. These particular conveyor constructions generally are not intended for use in harsh environments and for extremely long belt runs as found in mines and similar locations due to their expensive construction and configurations.
Accordingly, the need has existed for a belt conveyor idler which is extremely simple and inexpensive in construction, which provides a low-friction support for the upper and lower belt runs, which is free of moving parts, and which requires no lubrication for its operation.